[cfe-dev] clang windows: clang-cl support for /MP

[Kim Gräsman]

There are two levels of parallellization in Visual Studio/Visual C++;

1) Machine-wide setting of how many projects to build in parallel --
this informs Visual Studio/MSBuild
2) Compiler setting (/MP) of how many source files to compile in
parallel -- this actually informs CL.EXE and causes it to launch child
processes

See Bruce Dawson's treatise for the gory details:
https://randomascii.wordpress.com/2014/03/22/make-vc-compiles-fast-through-parallel-compilation/

Not sure how easy/desirable this behavior would be in clang-cl, but
from a principal standpoint I'd prefer this kind of thing in the build
system, not the compiler.

- Kim


On Wed, May 20, 2015 at 12:12 PM, Nikola Smiljanic <popizdeh at gmail.com> wrote:
> This is usually handled by the build system (make -j, ninja, etc.). I'd
> expect this flag to actually control MSBuild, not the driver, but it'd be
> interesting to find out how it really works.
>
> On Wed, May 20, 2015 at 6:01 PM, Tilo Kühn <tilo.kuehn.73 at googlemail.com>
> wrote:
>>
>> are there any plans to support the /MP option (parallel compilation within
>> one project) in clang-cl?
>> at the moment clang for windows prints out a warning that the option is
>> not supported yet and it uses only one core while compiling a single
>> project.
>>
>> (if msvc is allowed to compile parallel independent projects it uses a
>> multiple cores.)
>>
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